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Time to post the conclusion to my first adventure into the land of RAID 5. I wrote last week that I got a report from RAID Utility in Mac OS X that one of my drives had failed. I mentioned that I had a spare matching drive on hand. I got the Mac Pro with 1 stock Apple-installed 750GB drive, and bought 4 more, from Other World Computing (a.k.a. macsales.com). I installed three of the drives into the tower and allowed the boot drive to be the boot drive and set up the other three drives as a RAID 5 array to act as my primary project scratch disc. One of the drives failed (the warranteed replacement is already on the way to me from OWC), and when I left you, I was shutting down to perform the extraction and replacement.

For a great layout on the different levels of RAID and what RAID is all about, check out wikipedia.

Well, I did just that. I shut the machine down and let it cool for 5-10 minutes as recommended. Then I removed all of the connection cables to the machine (may not have had to remove more than just the power), and opened the box up. It's nice that RAID Utility told me one of my drives had failed, but unfortunately it didn't tell me explicitly which one had failed - the only clue I had was in the list on the left. The list of drives only showed that drives in Bay 1, Bay 2 and Bay 4 were A-Ok. I deduced, due to my high level math and counting skills, that the drive in Bay 3 was the one that had bowed out since it was missing from the list, and Apple is kind enough to number the drive sleds in the Mac Pro, so I was reasonably confident that I had figured out which one needed replacing. I easily removed the drive in Bay 3 (ouch, those little release bars pinch like hell), unscrewed it from its sled, screwed in the new drive, popped it in on the sled, closed the machine up, plugged the connectors back in, and rebooted.

The first thing that happened was kind of confusing. RAID Utility reported the same error again, making my heart stop a little bit... I thought yet ANOTHER drive had keeled. Turned out RAID Utility was just automatically reporting any existing trouble as it does whenever you boot up and there is any kind of issue in the RAID realm. In fact, after I calmed down, I realized that there were multiple dialog boxes awaiting clicks that had been thrown up by RAID Utility. The second dialog told me that a drive which had been previously assigned to part of my RAID 5 (RS1) had been removed, and a third dialog reported that a brand new drive had been detected. I OK'ed (actually, I think it's a "continue..." button) all those boxes and got back to the main RAID Utility window. I didn't see RAID Utility doing anything automatically in terms of a RAID rebuild, so I started poking around menus. Turns out the process is a little non-intuitive.

I saw that there was now a drive in Bay 3 in the list on the left, and it had a green light, and that was nice to see. What I figured out by giving Apple Care a quick call (those folks are so damn helpful!) was that I needed to click on the Bay 3 drive, and then choose "Make Spare" from the RAID menu within RAID Utility, giving this drive a new status as far as my RAID Set 1 (RS1) was concerned. As soon as it was marked as a "Spare," RAID Utility immediately took it over, and began the multi hour process of rebuilding my RAID in the background. I was able to use the RAID itself and all of the files on it throughout this entire process, so if I had known that "Make Spare" was the needed step for getting my RS1 to recognize the new drive and start sharing data with it, the whole process would have taken me about 6 minutes. Now I know, and now you know, too. See how this works?

The process completed, I got a nice friendly message in RAID Utility, "RAID Set 1 redundancy restored," and I smiled. So far so good, OWC is sending me a new drive, and all is well in Wellsville. The only thing that can kill you with RAID 5 in my estimation is to have a second drive kiss dirt before you can replace the first one in that case. you lose your RAID entirely. I guess no matter what solution one uses, one still needs to back all of one's stuff up, off site, to be truly protected from catastrophic data loss. But I will say that RAID 5 is a good start toward protecting myself from being down for more than a couple of minutes right in the middle of a client project. This whole thing is a really nice implementation, and I recommend using it if you are in need of a RAID and aren't sure whether to go for it or not.